Mechanical refrigerators, including those of the air-blast type, have long been used for cooling and freezing articles, such as food products. More recently, systems employing a cryogen, such as liquid nitrogen or liquid carbon dioxide, have become commercially important, particularly in the food market. Carbon dioxide is excellently suited for the cooling and/or freezing of food material because it exhibits the advantages of exceptional cooling efficiency at a temperature which is relatively close to the freezing point of water and thus does not cause fracturing problems in the surface of food products.
Various systems have been developed to utilize the refrigeration advantages of carbon dioxide, and U.S. Pat. No. 3,815,377, issued June 11, 1974 to Lewis Tyree, Jr., discloses an insulated freezing tunnel designed for using carbon dioxide to freeze food articles being carried along an endless conveyor. The patent discloses a particularly efficient snow-making system wherein overhead nozzles are employed to direct a spray of carbon dioxide snow particles and cold vapor downward onto the food articles being transported therepast upon the endless conveyor. Improvements in cooling and/or freezing systems of this type which will perform more economically and/or efficiently are constantly being sought after.